1. FIELD OF THE INVENTION
The present invention relates generally to photography and more particularly it relates to a novel method of adding organic compounds useful in photography to photosensitive emulsions necessary for producing photographic materials.
2. DESCRIPTION OF THE PRIOR ART
Fine silver halide crystals, zinc oxide, cadmium sulfide, fine titanium oxide crystals, etc., are generally known as light-sensitive elements dispersed in photographic emulsions. Also, various compounds are added to each photographic emulsion for various purposes. In particular, photographic compounds for photography added to silver halide photosensitive emulsions include chemical sensitizers, antioxidants, antistatic agents, optical whitening agents, ultraviolet absorbents, plasticizers, development accelerators, color toning agents, supersensitizing dyes, antihalation dyes, filter dyes, antiirradiation dyes, color couplers, coating aids, hardening agents, etc.
The term "organic compounds useful in photography" or "organic compounds useful in photographic materials" as used in this specification means organic compounds other than spectral sensitizing dyes added to photographic materials, for instance, to silver halide photosensitive emulsion layers, intermediate layers, subbing layers, protective layers, filter layers, antihalation layers, etc.
Various methods have been known for adding the organic compounds useful in photography to photosensitive emulsions. For instance, a method in which the organic compound is added as a solution in an organic solvent such as methanol, ethanol, etc., a method in which the organic compound is added as a solution in a mixture of an organic solvent and water, a method in which the organic compound is added as a solution in an aqueous medium such as water, an alkaline aqueous solution, an acid aqueous solution, etc., a method in which, in the case of adding, for instance, a water-insoluble color coupler to a silver halide emulsion, the color coupler is dissolved in a water-immiscible oily solvent and the coupler solution is dispersed in the silver halide emulsion directly or after dispersing the coupler solution in an aqueous gelatin solution together with a dispersing agent, an the like, are known.
However, these known methods have various disadvantages. That is, in the method of adding the organic compound as a solution in a water-miscible organic solvent, when the solubility of the organic compound in the organic solvent is low, a large amount of the organic solvent is required, which results in reducing the surface activity of a coating aid present together in the photographic emulsion, coagulating a binder in the emulsion, and further, in the case of a color photographic material, aggregating other photographic additives such as a coupler, etc., present together with it in the photographic emulsion. Moreover, in such case the difficulties which occur make high speed coating of the photographic emulsion, for instance, coating of the emulsion at a speed of higher than 100 meters per minute very difficult.
On the other hand, the method in which a coupler is dissolved in a water-immiscible oily solvent, the coupler solution is dispersed in an aqueous solution of a hydrophilic colloid together with a dispersing agent, and the dispersion is added to a silver halide emulsion has the disadvantage that when the photographic material prepared by coating the silver halide emulsion containing the dispersion is processed with a photographic processing composition, the evaluation of the emulsion is difficult until the photographic material is dried since the photographic material is opaque in a wet state. Also, since the gelatin layer of the aforesaid photographic material is very soft, precautions are required for the treatment of the photographic material during processing and drying of it.